Mammalian reproduction is under the control of pituitary gonadotropins, luteinizing hormone (LH) and follicle stimulating hormone (FSH), which are composed of a common alpha subunit and a specific beta subunit. All 3 gonadotropin genes are regulated by gonadotropin-releasing hormone (GnRH), which is secreted from the hypothalamus in a pulsatile manner (critical to its effect on gonadotropin secretion and gene expression). The pattern of GnRH pulsatile stimulation (amplitude and frequency) has been shown to regulate the expression of the LH and FSH subunit genes in either a coordinate or differential manner. Of particular importance, we have recently shown that testosterone (T) plays a key role in GnRH action, being required for pulsatile GnRH to acutely (within 6h) increase LH beta mRNA expression in the female rat. Similar to GnRH, the pattern of second messenger signals (pulsatile vs continuous) can also regulate LH and FSH subunit mRNAs, suggesting that alterations in second messenger in second messenger activity may play a role in the transduction of GnRH pulse patterns from the plasma membrane to athe nucleus. The aim of this proposal is to determine the role played by alterations in input signal patterns (GnRH, second messengers) in the regulation of gonadotropin subunit and GnRH receptor gene expression in the female rat in vitro, with specific emphasis placed on transcriptional regulation. These studies will also characterize the role of T in facilitating GnRH actions on LH beta mRNA expression. Other studies will focus on the effect of GnRH on critical sites in the intracellular signal transduction pathway (i.e. activation of specific protein kinases), to determine whether altering the GnRH pulse pattern activate protein kinases in a selective manner. These results may provide a link between GnRH pulse patterns, activation state of specific protein kinases and gonadotrope gene expression. In humans and in most species studied, the pattern of GnRH pulse secretion changes during puberty, as well as during the menstrual cycle. These changes play an important role in previously described alterations in the ratio of LH/FSH secretory activity, believed to be critical during sexual maturation and follicular developments. Data suggest that various forms of anovulation in woman may result from abnormalities of GnRH pulse patterns. Specifically, GnRH pulse frequency is slow in hypothalamic amenorrhea (HA) and rapid in polycystic ovarian disease (PCO), compared to patterns seen in normal woman. Our in vitro studies would suggest that GnRH pulse pattern can selectively alter gonadotropin subunit gene expression. This effect may play a role in the increased serum FSH:LH in HA and conversely LH more than FSH in PCO. Thus increasing our knowledge of the intracellular mechanisms involved in the transduction of GnRH signal pattern may provide insights into normal female reproductive physiology leading to improved treatment of human infertility.